Carbon-coated carbon fabrics have found wide application, including friction applications, in the aerospace and missile industries, due primarily to their light weight, stability and stiffness at high temperatures. These materials are produced by resin-impregnation or chemical vapor deposition methods. Materials made via resin-impregnation include multiple carbon fabric layers which are impregnated with resin, molded to a thickness between 0.25 and 2 inches, and slowly carbonized at high temperature. Carbon-coated carbon fabrics made via chemical vapor deposition (CVD) typically comprise multiple layers of a porous material on which elemental graphitic carbon is deposited by pyrolysis of a hydrocarbon gas into its constituent elements. The physical properties of such carbon fabrics depend upon both the number of plies used and the amount of graphitic carbon present. For example, structural applications typically employ a material comprising multiple fabric layers which have been subjected to repeated CVD cycles, resulting in a dense, rigid material.
More recently, a wet friction application for a single layer of a carbon-coated carbon fabric, formed by CVD, was developed to solve automotive friction material performance problems. U.S. Pat. No. 4,700,823, issued to Winckler, discloses a CVD-coated carbon fabric for use in wet friction applications in automobile components. This material was formed by the general method disclosed in U.S. Pat. No. 3,944,686, issued to Froberg. Winckler teaches that CVD coating of a carbon mesh fabric for a relatively short period of time, such as several minutes, results in a flexible, porous material suitable for use in wet friction applications requiring a thin friction material, such as in a wet clutch or brake.
Despite the advance in the art represented by the disclosure of Winckler, currently available carbon-coated carbon fabrics continue to present disadvantages. For example, the CVD fabric is produced in large batch CVD furnaces which increase production costs significantly. This equipment is very expensive and, even with relatively short processing times, the method consumes significant amounts of energy due to the high temperatures and low pressures required. The CVD process also yields a non-uniform deposition of carbon on the fabric.
Consequently, there is a need for a carbon-coated carbon fabric suitable for use in wet friction applications which overcomes the disadvantages of the prior art materials. Also needed is a faster, more uniform and less expensive method for producing such a material.